Dayia is a recently described genus of Polemoniaceae. Based on the circumscription of Porter & Johnson (2000) Dayia is restricted to northern Baja California Sur, Mexico, on both the Pacific and Gulf of California coastal regions. Porter and Johnson included two species, Gilia scabra Brandegee, and a newly described one, D. grantii. Below, I provide a description of the genus, as well as a key to distinguish the two species.

The generic name Dayia, honors Alva G. Day, botanist and student of Polemoniaceae.

Dayia is similar in general appearance to both Ipomopsis and Giliastrum; however, morphological data, as well chromosome number, provide evidence that it is isolated from these genera. The haploid chromosome counts (from dividing pollen mother cells) of D. scabra and D. grantii are n= 9. This contrasts with all known members of Ipomopsis, which possess a base chromosome number of n= 7 (Grant 1959). Pollen of both D. scabra and D. grantii is blue, with a thick striate-reticulate exine; seeds are minute; and a well-developed corolla tube (6–9 mm long; longer than the calyx) is present. This differs from all members of Giliastrum, having yellow, pertectate pollen grains, larger seeds, and a very short corolla tube (less than 5 mm long; shorter than the calyx).

Dayia is the subject of active research. Evidence in hand supports the expansion of Dayia to include three additional species. This being the case, the information here will soon be obsolete, as the generic description will need to be modified to account for these additional species and the key (below) will also change. These changes are expected soon!